Two sets of confidential blueprints for the planned Freedom Tower, which is set to rise at Ground Zero, were carelessly dumped in a city garbage can on the corner of West Houston and Sullivan streets, The Post has learned.

Experts said the detailed, floor-by-floor schematics contain enough detail for terrorists to plot a devastating attack.

"Secure Document - Confidential," warns the title page on each of the two copies of the 150-page schematic that a homeless, recovering drug addict discovered in the public trash can.

"Any time a sensitive document is unintentionally left behind, it's a treasure trove for a potential adversary," aid Robert Strang, CEO of Investigative Management Group, a global security firm. "It enables them to look for vulnerabilities in design that they can target - an age-old military tactic."

Informed of what the homeless man, Mike Fleming, had found, shocked Port Authority officials called it an egregious security lapse.

"Violating these protocols is cause for serious disciplinary action - up to termination for employees and breach of contract and legal action for contractors," said Candace McAdams, PA director of media relations.

One of the identical sets was missing the first 14 pages, which is particularly alarming.

Besides the PA, there are 11 entities listed on each page of the blueprints, including the builder, Tishman Construction, and architects Skidmore Owings and Merrill.

Although the documents, dated Oct. 5, 2007, are not a complete set of blueprints, they do contain details such as plans for each floor, the thickness of the concrete-core wall and the location of air ducts, elevators, electrical systems and support columns.

"Certainly, if you know the thickness of concrete, someone with an explosive background can develop and plot an attack," Strang said.

That was exactly the thought that ran through Fleming's mind when he found the documents and alerted The Post.

Fleming, 28, originally from Ohio, said he was rummaging through the garbage in search of cardboard, "because the concrete is so cold to sleep on," when he noticed the documents and the warning to "properly destroy if discarded."